Fedora 42 ships with bleeding-edge tech, but if you’re a Java developer who wants to run the latest LTS version (Java 21)—or switch between Oracle JDK and OpenJDK—you’ll need to get your hands a bit dirty.

In this guide, we’ll cover:

• ✅ Installing OpenJDK 21 using DNF (Fedora’s package manager)
• ✅ Installing Oracle JDK 21 manually from Oracle’s site
• ✅ Switching between Java versions using the alternatives command

Let’s dive in.

🧰 Prerequisites

Make sure you’re running Fedora 42, and you’ve got sudo privileges. Open your terminal and run:

cat /etc/fedora-release

You should see something like:

Fedora release 42 (Adams)

🔧 Install OpenJDK 21 using DNF

Fedora’s default repositories offer OpenJDK 21. Run:

sudo dnf install java-21-openjdk java-21-openjdk-devel

Verify installation:

java -version

Expected output:

openjdk version "21" ...

☕ Install Oracle JDK 21 (Manual)

Oracle JDK isn’t in Fedora’s repos due to licensing, so we’ll do a manual install.

Step 1: Download Oracle JDK 21

Go to Oracle’s official JDK page: 👉 https://www.oracle.com/java/technologies/javase/jdk21-archive-downloads.html

Download the RPM file

Step 2: Extract and Move to /opt

cd ~/Downloads
sudo rpm -Uhv jdk*-linux-x64_bin.rpm

(replace actual file name)

🔄 Switching Between Java Versions with alternatives

Fedora uses alternatives to manage multiple versions of the same tool.

Use alternatives to Choose Your Default

To select which Java runtime you want:

sudo alternatives --config java

You’ll see:

There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
*+ 1           /usr/lib/jvm/java-21-openjdk/bin/java
   2           /opt/jdk-21/bin/java

Enter to keep the current selection[+], or type selection number:

Choose the one you want. Repeat the same for javac:

sudo alternatives --config javac

✅ Verify It Works

java -version
javac -version

You should now see whichever JDK you selected as the output.

📌 Pro Tip: Set JAVA_HOME in .bashrc or .zshrc

Add this to your shell config to avoid issues with Maven, Gradle, etc.

For Oracle JDK:

export JAVA_HOME=/opt/jdk-21
export PATH=$JAVA_HOME/bin:$PATH

For OpenJDK:

export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
export PATH=$JAVA_HOME/bin:$PATH

Then:

source ~/.bashrc  # or ~/.zshrc

🚀 Wrapping Up

You now have both OpenJDK 21 and Oracle JDK 21 installed on Fedora 42, and you know how to switch between them cleanly using alternatives.

If you’re working on different projects or enterprise apps that require Oracle JDK, this setup gives you flexibility without compromising the Fedora way.